1. Field of the Invention
The present invention relates to a continuously variable speed converter and, more particularly, to such a converter of the friction type for cooperative use with a fluid pump driven by an engine of a motor vehicle.
2. Description of the Prior Art
In a continuously variable speed converter known heretofore, as shown in FIG. 1, a pair of friction discs 4 and 5 are carried respectively on axially aligned input and output shafts 1 and 2 and, at guide ways 4a and 5a formed respectively thereon, are in contact with power-transmission balls 3, the rotational axis of each of which is angularly adjustable. Further, a pressuring ring 8 is keyed on each of the shafts 1 and 2 to define between itself and the associated disc 4 or 5 a plurality of circumferentially continued rhomboid grooves 7, in each of which a pressuring ball 6 is contained. These grooves 7 and balls 6 constitute a pressuring device, which serves to automatically adjust the contact pressure between the associated discs 4 and 5 and the power-transmission balls 3. Namely, when rotational torque which corresponds to the load on the output shaft 2 acts on the pressuring device thereof, the pressuring balls 6 ride up on the slopes of the grooves 7, generating a thrust force based upon such wedge action and, in consequence, the associated discs 4 and 5 pressure the balls 3 to thereby adjust the contact pressure therebetween.
In the speed converter, the rotational torque acting on the input shaft 1 becomes larger than that acting on the output shaft 2 when the output/input speed ratio is more than 1, while rotational torque acting on the output shaft 2 becomes larger than that acting on the input shaft 1 when the speed ratio is less than 1, and in order to generate thrust force corresponding to the larger rotational torque, therefore, such a pressuring device has to be provided on each of the input and output shafts 1 and 2. This undesirably makes the construction complicated and invites increases of manufacturing costs because of the difficulty in machining the rhomboid grooves. In addition, since the slopes of the rhomboid grooves 7 suffer from wear by the action of great thrust force, problems in maintenance remain unsolved.